This invention is related to wax-containing petroleum distillate having improved low temperature flow properties. More specifically, the present invention is related to a wax-containing middle distillate fuel oil having a boiling range within the limits of about 120.degree. and about 400.degree. C.
The problem of improving the cold flow properties of wax-containing distillates has become more pronounced recently because of increases in the demand for certain petroleum products, including kerosene and the middle distillates. Kerosene, which acts as a solvent for n-paraffin wax, normally had been a component of middle distillate fuel oils. The increased demand for kerosene in jet fuels has reduced the amount of kerosene available for use in middle distillate fuel oils. In addition, the increased demand for middle distillate fuel oils, particularly diesel fuel, while demand for gasoline has remained essentially flat, has made it attractive to maximize the production of middle distillates.
The wax present in middle distillates precipitates at low temperature, forming large waxy crystals which tend to plug the small pore openings of fuel filters. This problem is particularly acute for diesel fuels, where the openings in the fuel filter typically are between about 5.0 and about 50 microns. Conventional pour depressants, which lower the pour point, i.e., the point at which the fuel can no longer be poured, may not be completely satisfactory for preventing pluggage of the fuel filters. While pour depressants often prevent the fuel from setting up as a gel, large wax crystals may be formed. However, to improve the cold flow properties of wax-containing middle distillate fuels oils so that the wax does not plug the fuel filter pores, it is necessary that fine wax crystals be formed.
Considerable work has been directed at additives which improve the cold flow properties of the wax-containing middle distillate fuels. U.S. Pat. No. 3,790,359 is directed at the addition of from about 0.1 to about 3 weight percent of an essentially saturated hydrocarbon fraction substantially free of normal paraffinic hydrocarbons having a number average molecular weight in the range of about 600 to about 3,000, in combination with a copolymer of ethylene and an unsaturated ester, where the copolymer has less than 6 methyl terminating side branches per 100 methylene groups. The weight ratio of the saturated hydrocarbon fraction to the copolymer was disclosed to range between about 25:1 to about 1:1.
U.S. Pat. No. 3,999,960 discloses the use of ethers, particularly alkyldiphenylether, to improve the cold flow properties of wax-containing middle distillate fuels.
However, the continuing increase in diesel fuel may require the use of middle distillates having still greater n-paraffin wax contents. Frequently these fuels having high wax appearance points (WAP) do not respond well even to combinations, such as those previously noted.
Accordingly, it is desirable to provide an additive combination which is effective in improving the cold flow properties of middle distillate fuels having relatively high WAP values.
It is also desirable to provide a process in which the additive combination can be used in a relatively low concentration.
It would also be advantageous to utilize an additive combination which is relatively inexpensive.
It also would be advantageous to employ an additive combination which did not adversely affect the combustion properties of the fuel.
The present invention is directed at a wax-containing middle distillate fuel oil having added thereto to improve the low temperature flow properties the combination of:
(a) an amorphous, normally solid, essentially saturated hydrocarbon substantially free of paraffins;
(b) a copolymer of ethylene and an unsaturated ester; and
(c) an ether.